In general, a backlight unit (BLU) is a light source device disposed behind a liquid crystal screen to emit light to the liquid crystal screen such as a liquid crystal display (LCD), and uses light emitting diodes (LEDs) as a light source. When LEDs are used as a light source, the backlight unit uses a red (R) or green (G) fluorescent material on a blue (B) LED chip to emit white light.
Recently, a backlight unit configured to emit white light using a quantum dot sheet 4 has been proposed (see FIG. 1). Since white light realized through the quantum dot sheet has excellent color expression in comparison to white light realized through existing blue LED chips and fluorescent materials, production of backlight units using the quantum dot sheet is gradually increasing.
Generally, as schematically shown in FIG. 1, a backlight unit that adopts a quantum dot sheet includes a light guide plate 1, an LED light source 2 disposed on a side surface of the light guide plate 1, a reflective plate 3 disposed under the light guide plate 1, and a quantum dot sheet 4, a diffusion sheet 5, and a prism sheet 6 sequentially laminated on the light guide plate, so that the backlight unit may emit white light.
For example, when the LED light source 2 is a B LED, the quantum dot sheet 4 including quantum dots configured to emit R and G light is used. Referring to FIG. 2, the quantum dot sheet 4 includes a quantum dot layer 4a in which quantum dots are distributed and barrier layers 4b configured to cover upper and lower surfaces of the quantum dot layer 4a. The barrier layers 4b block moisture and air from entering the quantum dot layer 4a, and the quantum dot sheet 4 has a structure in which the barrier layers 4b are adhered to the upper and lower surfaces of the quantum dot layer 4a, and adhesive layers 4c are additionally provided between the quantum dot layer 4a and the barrier layers 4b. The adhesive layer 4c decreases light transmittance and light efficiency, and a manufacturing process is complicated, and thus manufacturing cost is increased.
In addition, in the quantum dot sheet 4, after the quantum dot layer 4a is formed, the quantum dot layer 4a comes into contact with air and is oxidized in a process of bonding the barrier layers 4b to the upper and lower surfaces of the quantum dot layer 4a, and the thickness of the quantum dot layer becomes thick, which makes it difficult to form the quantum dot sheet 4 into a slim structure, such that the volume and/or a thickness of the backlight unit is increased.
Further, the existing quantum dot sheet 4 may have entangled or aggregated quantum dots in the quantum dot layer 4a, such that intrinsic properties of the quantum dots are degraded, and a defect of light being unable to be uniformly emitted may frequently occur. In order to solve this problem, the quantum dot layer 4a has to contain more quantum dots than a required reference value, which results in increasing the manufacturing cost of the quantum dot sheet.
Therefore, it is necessary to develop a new quantum dot sheet in which blue light can be converted into white light with high efficiency so that the quantum dot sheet has superior color reproducibility and a slim structure.